In recent years, with the development of medicinal chemistry and biochemistry, the demand for optically active organic compounds has been largely growing. This is because many new, high-effective drugs belong to optically active compounds with chiral centers; on the other hand, studies on these drugs show that only one type of optical isomer with certain configuration has the pharmacological activity; while another type of optical isomer may have no any pharmacological activity, and even have toxic or side effects to human beings. One way to get optically pure active enantiomers is the resolution of racemates, whereas the operation of this method is extremely cumbersome, and only a small amount can be handled; Another way is utilization of asymmetric synthesis, which can directly obtain optically active compound with a single configuration. Asymmetric catalysis has been received increasing attention due to its simple process and high efficiency. Recently, many new types of chiral transition metal complexes with high catalytic activity and stereoselectivity have been successfully synthesized, which largely improve the chemical and optical yields of chiral products. Therefore, asymmetric catalysis exhibits a broad prospect and a great power in the synthesis of optically active compounds.
So far, most of the asymmetric reactions are catalyzed by homogeneous catalysts, and the catalysts are mostly chiral transition metal complexes. Amino acids and their derivatives proceed many advantages as the chiral ligands of metal complex catalysts: 1. their structures are easy to be functioned; 2. natural chiral amino acids are cheap and easy to get, and also have a wide range of types; 3. they have a high optical activity and their derivatization are easy to be achieved; 4. the polarization, pH value, and molecular size are easy to modulate; 5. selected metal centers can be in a wide range, and different kinds of metal centers are available in catalyzing different types of asymmetric catalytic reactions, etc. Therefore, studies on using amino acids as chiral ligands have been gradually developed, and good results have been obtained in several respects.
Layered double hydroxides (LDHs), also known as hydrotalcite, are known as a kind of new multifunctional layered materials. Due to its unique characteristics of the composition and structure, such as ordered bi-dimensional layered structure, highly chemical stability, adjustable metal composition in the LDHs layers, exchangeable interlayer anions (a variety of functional anions can be exchanged into the interlayer space). A variety of functional composite materials can thus be constructed. Metal complexes with catalytic properties can be intercalated into LDHs layers by ion-exchange, which avoids multiple steps of covalent ligand modification; moreover, bi-dimensional open space between the adjacent LDH layers is beneficial to take advantage of the interlayer catalysts and exhibit high catalytic activity and selectivity.